Dissertação de mestrado integrado em Engenharia Biomédica (área de especialização em Engenharia Clínica) ; Group A rotaviruses are the leading cause of severe diarrhoea in children under 5 years of age worldwide, accounting for approximately 600,000 child deaths each year. Two rotavirus vaccines, Rotarix® and RotaTeq®, have been licensed in Belgium, and they have strongly reduced the disease caused by rotavirus infections. However, the rotavirus seasons following Rotarix® introduction in 2006 were marked by a relative increase of G2P[4] rotavirus strain prevalence, when compared with seasons before vaccine introduction. The goal of the work described in this thesis was to perform an epidemiological study on rotavirus prevalence and genotype distribution in Belgium in the 2009-2010 season, as well as to determine if this relative increase in G2P[4] strains is a vaccinerelated event or the result of usual genotype fluctuations. A total of 577 stool samples collected from Belgian paediatric patients between August 2009 and July 2010 were analysed, from which 491 samples were positive for rotavirus and further characterised. The most prevalent rotavirus genotype was G2 (61.9%), followed by G1 (25.3%), G4 (3.7%), G9 (3.3%), G12 (2.9%), G3 (1.8%), and G6 (0.4%). Overall, G1, G3, G4, G9 and G12 were mainly associated with the P[8] genotype, whereas all G2 were exclusively associated with P[4]. The majority of the positive samples came from the north of Belgium, especially from the provinces of Antwerp (43.3%), Flemish Brabant (18.2%) and East-Flanders (17.9%). The 2009-2010 season is now the fourth season after Rotarix® introduction in which we observe a further increase on the relative prevalence of G2P[4] strains, suggesting that vaccination might be one of the factors influencing rotavirus genotype distribution, thereby allowing the emergence of G2P[4] strains. The phylogenetic analysis showed that several lineages of G2P[4] were co-circulating in 2009-2010. Geographic distribution of these lineages revealed no ...